Definition of thro' in English:

thro'

preposition, adverb, & adjective

literary, informal
non-standard spelling of through
‘Friendship, dearest creatures, will make at pleasure a safe bridge over the narrow seas; it will cut an easy passage thro' rocks and mountains, and make England and Italy one country.’
non-standard spelling of through
‘I have to worry thro' thick and thin to get all my clothes, crockery, chairs, clock, and so on.’

Pronunciation

thro'

/θruː/